Update git refs

1) Update remoteRefs whenever fetched.
2) Request remote_refs async on "Git Branch" action. Local copy is returned immediately.

fixes #2346 

@dinhviethoa PTAL thanks.

We need to move Fetch.updateAndGetRemoteRefs(options); somewhere else.

- Ideally, the dialog would get the local cache and show it.
- Then, perform a network call in the background (show a progress to tell user that some information is still pending from the network),
- Then, update the UI when the network call is done.

Your current API doesn't allow to do it.
Please come up with something in the backende to be able to implement it even if the UI doesn't actually implement it.